1. Field of the Invention
The present invention relates to optical systems. More specifically, the present invention relates to lasers.
2. Description of Related Art
The implementation of compact transmitters ranging from flash ladar active sensors to high energy weapon-class laser systems is currently limited to large platforms due to the relatively low power per weight ratio numbers in the present approaches. Efficient diode laser pumped solid-state lasers have pushed the wall-plug efficiency to levels exceeding 25% and have scaled to multi-kilowatt powers in inherently compact systems for sensor transmitters and—ultimately—directed energy weapon implementation. Practical utility of diode-pumped lasers is still limited, however, by the need for extensive sophisticated thermal management infrastructures which add to the complexity, weight, and power of the overall laser system. This becomes especially important for spaceborne and airborne platforms where weight-volume envelopes need to be kept to a minimum. In addition, certain laser waveforms (such as high peak power—short pulse and low duty cycle) are not at all suited for diode pumping; however, the alternate flash lamp pumping approach is very inefficient in conventional lasers.
Flash lamp pumped lasers are widely used in today's industrial, medical and research laser systems. These lasers, however, are inherently inefficient because of the poor spectral overlap between the flash-lamp spectral emission and the absorption bands of REI (rare earth ion) doped insulating crystal hosts (such as Nd3+, Yb3+, Er3+, etc. in crystals, glass, polymers, etc.). Although efficient integrating pump cavities have been employed in order to bring the efficiencies of Nd:YAG lasers to as high as 3-4%, the significant waste heat loading in these lasers in addition to the poor efficiency prevents them from being scaled to compact high energy waveforms within compact architectures/geometries.
Sunlight pumped lasers have been studied and demonstrated; however, they also utilize conventional REI-doped insulating crystal hosts/gain media and therefore have limited efficiency due to the poor spectral overlap of the sun's blackbody emission and the relatively narrow absorption bands of REI ions.
Semiconductor (SC) lasers can be more efficient than REI-based lasers, but typically are not suitable for high energy/power scaling. Recent work on optically pumped semiconductor lasers and amplifiers in addition to optically pumped quantum dots (QDs) shows promise for directly pumped SC-based lasers. However, due to the extremely high saturation intensities of SC lasers, they are typically limited to micron-scale waveguide geometries and are not scalable to practical bulk high energy laser geometries.
Hence, a need exists in the art for an improved compact, lightweight laser that is scalable for high energy and power, and that offers higher efficiency than conventional approaches.